Pneumatic engine for mine hoist braking

ABSTRACT

Instead of using a single large pneumatic actuator for driving the brake shoes against the rotating brake surface, this invention uses a number of smaller pneumatic actuators, controlled individually and collectively by means of a regulator, for driving the shoes against the braking surfaces. The actuators are coupled with the brake shoes and the pneumatic fluid is controlled by the regulator such that one actuator normally applies the brakes for a medium or light braking effort and it is assisted by one or more of the other actuators when the braking effort required is greater than the one can deliver. In some instances, it may be desirable to construct the actuator as a single multistage unit wherein one stage is in command of the braking and is assisted by the others whenever necessary. The braking equipment also includes the well-known falling weight for emergency application of the brakes in the event of loss of the pneumatic fluid; otherwise the weight plays no part in the braking operation.

United States- Patent Inventor Peter De Hertel Eastcott Peterborough,Ontario, Canada Appl. No. 859,345

Filed Sept. 19, 1969 Patented May 18, 1971 Assignee Canadian GeneralElectric Company Limited Toronto, Ontario, Canada PNEUMATIC ENGINE FORMINE H0181 BRAKING 13 Claims, 1 Drawing Fig.

3,181,665 /1965 Trombetta ABSTRACT: Instead of using a single largepneumatic actuator for driving the brake shoes against the rotatingbrake surface, this invention uses a number of smaller pneumaticactuators, controlled individually and collectively by means of aregulator, for driving the shoes against the braking surfaces. Theactuators are coupled with the brake shoes and the pneumatic fluid iscontrolled by the regulator such that one actuator normally applies thebrakes for a medium or light braking effort and it is assisted by one ormore of the other actuators when the braking effort required is greaterthan the one can deliver. In some instances, it may be desirable toconstruct the actuator as a single multistage unit wherein one stage isin command of the braking and is assisted by the others whenevernecessary. The braking equipment also includes the wellknown fallingweight for emergency application of the brakes in the event of loss ofthe pneumatic fluid; otherwise the weight plays no part in the brakingoperation.

BATTERY 24 V. D.C.

39 I 75 CROSS T 22 l'ln 24 ENGINE 25 73 2 l REGULATOR I 2 PANEL 8 l2 4 g10 TOPARTNER $3 EDECELERATION i ENGINE j E, 56 E REGULATOR a 49 i 59 v66 51 52 Lu 5 i 48 7 53 MANUAL BRAKE 13 6O LEVER TO SERVO 'lli L19 l 5558 VALVE OF 47 PARTNER 71. r" BRAKE ENGINE 71 STABILIZING SERVO 7o TANK68 45 40 /77s 29 COMPRESSED 17 AIR STORAGE TANK FALLING WEIGHT (BACK-UP) PATENTEU HAY'I 8 I97} BATTERY 24v.-

a 1 is Q m U OFR R E mmm mm MBL fiM p g R Q mm mum o v. m R R $O E D mmmmm, 3 PE 6 8 w |--.l. x I l 8 k ml? B 2 5 O R M 9 A m WE BRAKE ENGINESTABI LIZING TANK COMPRESSED AIR STORAGE TANK w. GTmH Wmw w IK MEC vFwmm PETER deH. EASTCOTT Ahcnt PNEUMATIC ENGINE FOR MINE H0181 BRAKINGThis invention relates to pneumatic braking systems, and in particularto braking systems for mine hoists.

As is well known a mine hoist is subjected to very severe loading,varying from one extreme of an empty conveyance at the mine head toanother extreme of a heavily loaded conveyance at the bottom of the mineshaft uncoupled from its counterbalancing conveyance. Whether the loadhe an empty conveyance, or a heavily loaded conveyance plus a longlength of rope, the lifting drive and the braking equipment must becapable of fast and efficient operation under all conditions, includingthe extremes which worsen as the depth of a mine increases. Thisintroduces innumerable problems in braking, the brakes being, of course,the most critical part of the hoist. They must be fail proof, or as nearthereto as possible, and they must also take over full control in theevent of a failure of the lifting device. Hence, adequate brakes underone set of operating conditions may be totally inadequate underdifferent conditions. For example, the rate that the brakes are appliedto control a heavy load in a suitable way will be far too severe for alight load, and a rate suitable for a light load will be insufficientfor a heavy load. Most of the braking is done during normal operatingconditions when the conveyances are coupled together, one acting as acounterbalance for the other. When hoisting is changed from one level toanother, conditions are abnormal in the sense that the cable windingdrums must be uncoupled and braked individually. This calls for muchmore braking capacity than is necessary for balanced hoisting. As aresult, the brakes are generally designed for abnormal conditions andadapted for the best performance possible under normal and lightoperating conditrons.

Braking equipment designed according to this invention retains the priorart capabilities of coping adequately with the abnormal conditions andyet improves the braking per formance during normal and light loads.Instead of using a single large pneumatic actuator for driving the brakeshoes against the rotating brake surface, this invention uses a numberof smaller pneumatic actuators, controlled individually and collectivelyby means of a regulator, for driving the shoes against the brakingsurface. The actuators are coupled with the brake shoes and thepneumatic fluid is controlled by the regulator such that one actuatornormally applies the brakes for a medium or light braking effort and itis assisted by one or more of the other actuators when the brakingeffort required is greater ta than one can deliver. ln some instances,it may be desirable to construct the actuator as a single multistageunit wherein one stage is in command of the braking and is assisted bythe others whenever necessary. The braking equipment also includes thewell known falling weight for emergency application of the brakes in theevent of loss of the pneumatic fluid; otherwise the weight plays no partin the braking operation.

The following detailed specification will aid in a fuller understandingof the invention when taken in conjunction with the appended diagram ofa mine hoist braking system.

Mine hoists of the drum winder type usually have two separateconveyances of which one acts as a counterbalance for the other. Thecable winding apparatus has two separate drums coupled together by meansof a clutch and the ropes oppositely wound on the drums so that as onedrum takes on tope the other lets out rope. Since one drum must becapable of operating alone while the other is braked for purposes ofchanging the operating'level, a braking engine is provided for each. Tochange levels, the operator uses the clutch to release one drum from thedrive and holds it stationary with its brake while he operates the otherdrum by means of the drive and its brake. The braking engine now to bedescribed is one of the two used with this kind of hoist. When the twodrums are coupled together, the operation will be referred tohereinafter as balanced hoistings," and when the two drums areuncoupled, the operation will be referred to as single line hoisting.This invention employs two levels of braking, one level for balancedoperation and another higher level for single line operation.

A preferred embodiment of the invention will now be described withreference to the drawings. ln this drawing there is shown the equipmentnecessary foroperating the brakes of one drum of a two drum winder, theother drum being braked in the same way by means of similar equipment.The equipment includes a pen pneumatic engine 8 coupled mechanically toa brake arm 9, a deceleration regulator 10, and manual control 11. Thepower drive of the engine consist essentially of two pneumatic brakeapplying cylinders 12 and 13, a pneumatic brake releasing cylinder 14, acompression coil spring 15 for priming the brakes, and a heavy weight 16held up in an elevated position by means of a pneumatic cylinder 17.Cylinders 12, 13 and 14 are held stationary in axial alignment and havetheir pistons 18, 19 and 20 attached to a common rod 21 which has aclevis 22 on its upper end pivotally connected to the outer end of arm9, i.e., right end, by means of a pin 23. Movement of pistons 18 and 19downward drives arm 9 clockwise to apply the brakes and movement of therod upward releases the brakes. The brake itself is well known,consisting of a brake drum 25 and a pair of brake shoes located onopposite sides of the drum, one of which is shown at 24. The lower endof the shoe pivots on a pin and the upper ends of the shoes areconnected to the inner end of the arm 9, shoe 24, directly and the othershoe through a tie rod 26. Hence, when the arm is turned clockwise shoe24 and its companion shoe are forced against brake drum 25, wherebybraking motion of the drum. Turning the arm counterclockwise causes theshoes to move away from the drum, releasing the brakes. Spring 15surrounds rod 21 and is compressed between the bottom end of cylinder 13and a collar 27 on the rod so that the energy stored in the springalways acts to apply the brakes. Cylinder 17 is mounted on a basestructure 28 with its axis vertical and has its piston 29 attached to arod 30 which hangs vertically downward from the piston and supportsweight 16 on its lower end. Air under pressure, in cylinder 17 under itspiston 29 holds the weight up; however, should this pressure be lost dueto a loss of pressure in the engine, the weight drops and applies thebrakes. This is an emergency device which stops the hoist and holds itstopped until the pressure is restored or other measures taken tooperate the brakes on an emergency basis. The falling of weight 16drives arm 9 clockwise through the following mechanism: an arm 31pivotally connected at one end 32 to rod 30 and at the other end 33 to astationary support 34; a rod 35 pivotally connected at its lower end 36to a midpoint of arm 31; and a clevis 37 secured to the upper end of therod and slotted at 38 for loosely receiving a pin 39 secured to theouter end of am 9. The slot and pin constitute a lost motion linkagewhich allows the braking arm to move freely of the emergency fallingweight mechanism during normal braking operations, but also allows theweight to apply the brakes after is has fallen a certain distance. r

The pneumatic equipment used in the engine with the double cylinderdrive will now be described. Whenever reference is made to a line thismeans an air line or pipe used for conveying air from one point toanother. Compressed air is supplied to a storage tank 40 by way of line41 from a suitable source of air compressed at a relatively highpressure. This air is led off line 41 into a line 42, through a valve 43which reduces the pressure of the air to about 70 p.s.i., into a line 44which branches off into two lines 45 and 46. Line 45 goes to anothertank 47 where a large volume of compressed air is stored at 70 psi. as astable source of air of the proper operating pressure, and line 47 goesto cylinder 17 on the under side of its piston 29 where the pressureacts on the piston to hold weight 16 up in its elevated position. Anoutlet line 38 from tank 47 branches off at 50 to engine 8 and at 49 toa similar engine for braking the other drum. This other engine is knownas the partner engine. Line 50 allows compressed air to flow directlyfrom tank 47 into cylinder 12 above its piston 18, and a takeoff line 51allows compressed air to flow directly from tank 47 into cylinder 13above its piston 19. Since the upper sides of these pistons are at alltimes exposed to the full thrust of the compressed air in tank 47, bothpistons are continually urged downward at the maximum push that thecompressed air is capable of. The force urging the pistons downward actson both pistons in a direction to apply the brakes i.e., it tends todrive rod 21 downward and thereby arm 9 clockwise. Hence the upper endsof the two cylinders are always charged for full braking by virtue oftheir direct connection to tank 47. Control of the braking applied iseffected through the control of the air to the under side of pistons 18and 19.

Numerals 52, 53 and 54 denote selector valves and numerals 55 and 56off-on valves. These are all two-position magnet valves which take theposition shown when electrically energized and their other positionswhen deenergized. In the energized portions shown, valve 52 connectsline 50 to the bottom end of cylinder 12, valve 53 connects line 57 toline 58, and valve 54 connects line 60 to the bottom end of cylinder 14;in their deenergized positions, valve 52 connects the bottom end ofcylinder 12 to line 57, valve 53 connects line 57 to line 59, and valve54 connects the bottom end of cylinder 14 to an exhaust outlet 61. Asclearly shown in the drawing line 60 is interconnected with line 57, andis connected to the bottom end of cylinder 13. In the energizedpositions shown, valve 55 is closed and valve 56 is open so as to iconnect line 60 to a line 62 going to the other braking engines;

in their deenergized positions valve 55 is open so as to vent the bottomends of cylinders 13 and 14 to the atmosphere through the exhaust outlet63, and valve 56 is closed. A normally open bleed valve 64 is closed byelectrically energizing its coil 65 from deceleration regulator so as toconnect line 59 to an outlet 66. This normally open valve is closed oncommand from regulator 10 by the energy applied to coil 65. A servovalve67 is connected to line 58 and to a line 68 communicating with the highpressure line 46, and has an exhaust outlet 69. It is operated by meansof compressed air, and its operation is controlled through manualcontrol 11 which is connected to line 68 and the servovalve via lines 70and 71 respectively.

Manual control valve 11 may be any one of a number of well knownmanually adjustable pressure regulating valves which receives air fromline 70 at high pressure and delivers this air to line 71 at a pressurereduced in direct proportion to the setting on its handle. This handleis movable manually between two extreme position; in one extremeposition the air in line 71 is at atmospheric pressure and in the otherextreme position it is at the full pressure in line 70. Hence, valve 11can increase the pressure in line 71 by moving its handle in thedirection which admits more air from line 70 and decrease this pressureby moving the handle in the other direction which exhausts air from line71 via the exhaust outlet 69. The air pressure in line 71 controlsservovalve 67, and it in turn controls the pressure of the air fed intoline 58 from line 68. Servovalve 67 is a volume amplifier whichcontinuously regulates the air pressure in line 58 according to thepilot pressure from line 71. An increase in pilot pressure causes theservovalve to increase the pressure in line 58 from line 68, and adecrease in pilot pressure causes the servovalve to decrease thepressure in line 58 by exhausting air from this line to the atmospherethrough outlet 69. Thus the air pressure in line 58 is essentiallyproportional to the position of the handle on valve 11 at all times.Another line 71a, carrying the same air pressure as line 71, goes to aservovalve like 67 for the partner engine.

During balanced hoisting the two braking engines operate together, butduring the time that the clutch is released the two engines operateindependently. The various modes of operation will now be outlined underdifferent headings.

MANUAL CONTROL In the condition illustrated in the drawing, the drumsare coupled together for balanced hoisting. Under these conditions,valves 52, 53, 54, 55 and 56 are energized and in the positions shown.As a result both engines operate together on their lower cylinders 13,the upper cylinders 12 being inactive because both ends of pistons 18are at full system pressure.

Assume now that the brakes are applied and the operator wishes torelease them. To do so he manipulates the lever of control 11 to theposition where it causes servovalve 67 to apply compressed air to thebottom ends of cylinders 13 and 14 at the pressure set by the lever.This air flows from tank 47 via lines 45, 46, and 68, servovalve 67,line 58, valve 53, lines 57 and 60 to cylinder 13 and valve 54 tocylinder 14. As compressed air is applied to the under side of piston19, its downward thrust decreases, relaxing the braking force applied toarm 9. When the pressures below and above piston 19 equalize, the onlybraking effort remaining is that due to spring 15 and the weight of arm9, rod 21 and pistons 18, 19 and 20. At this point, however, the lowerend of cylinder 14 is also at system pressure, and as a result itspiston 20 urges rod 21 upward against the force of spring 15 just enoughto free the brake shoes from the brake drum. To apply the brakes again,the operator manipulates the lever of control 11 into the position whereit causes the servovalve 67 to decrease the pressure in the bottom endsof cylinders 13 and 14 by allowing air to escape therefrom via valve 54,lines 60 and 57, valve 53, line 58, valve 67 and outlet 69. As thepressure below piston 19 decreases, the higher pressure above the pistonforces it down to apply the brakes again. Control 11 and servovalve 67are so designed that the air pressure can be accurately controlled sothat either releasing or applying the brakes will be as smooth as theskill of the operator. It is to be noted that during the normal brakingoperation just outlined that valve 56 remains open; as a result, thelower cylinder of the other braking engine operates in synchronism withcylinder 13, releasing or applying the brakes of the other drum insynchronism with braking operations of this drum.

1f the operator now wishes to change the level from which theconveyances operate, he locates the conveyance attached to one of thedrums at the new level, and follows certain procedural steps inrelocating the other conveyance. lnterlocking devices demand that thesesteps follow a particular pattern, which is general are as follows: lThe operator sets valves 52 in both engines so they activate the upperbrake cylinders, in which setting valve 52 connects the bottom end ofcylinder 12 to line 57. Cylinder 12 will now assist cylinder 13 in thebraking because its piston 18 is subjected to the same pressuredifferential as piston 19. (2) He applied the brake fully to both drumsby exhausting air from the bottom ends of both cylinders. (3) Heisolates the other braking engine from engine 8 by closing valve 56 andsetting any other controls provided for this purpose. (4) With the brakeshoes for drum 25 now clamped firmly on the drum by means of bothcylinders 12 and 13, he places the conveyance attached to the other drumin the proper location for balanced hoisting from the newly selectedlevel. (5) He engages the clutch and restores the system to its formerstate of single cylinder braking. The procedure outlines above, is, ofcourse, a gross over simplification of the actual situation; it isintended only to illustrate in a very general way the main purpose ofthe two cylinder braking engine. It requires very little knowledge ofhoisting to realize that much more braking effort is required foruncoupled drums than for counterbalanced drums; the second cylinder ineach engine supplies the additional effort. The application oftwo-cylinder braking is not necessarily restricted to level changing; itcan be applied whenever the operator feels that there is a need to doso.

EMERGENCY STOPPING The braking engines are designed for fail safeoperation under emergency conditions. (1) If the engine fails throughloss of its air pressure, the piston of cylinder 17 is no longer able tohold up weight 16. As the weight descends, it applies the brakes throughits mechanical linkage 30 to 39 with brake arm 9. (2) 1f the electricalpower from the main source fails a standby battery takes overimmediately and maintains normal braking operation for the emergencystop. (3) 1n the event that valves 52 to 55 should become deenergizedthrough failure of the battery as well, the main source valve52-connects the bottom end of cylinder 12 to line 57, valve 53 connectsline 57 to line 59 and thereby shuts off theair supply from line 58,valve 54 vents the bottom end of cylinder 14 to the atmosphere throughits outlet 61 and valve 55 vents the bottom ends of cylinders 12 and 13to the atmosphere through its outlet 63. This applies the brakes andstops the hoist, probably much more abruptly than otherwise This is ahighly unlikely situation indeed. In practice, emergency braking isrelatively complicated because numerous control devices become involvedin the process. A means for controlling the deceleration of the hoistwill be dealt with very briefly later under the next heading. Since fullparticulars on the various controls are not essential for anunderstanding of this invention, they have not been illustrated ordescribed.

DECELERATION REGULATOR Assume that during a winding cycle the controllersenses an overspeed above a set value. in response to this overspeed itinitiates an emergency braking operation which includes deenergizationvalves 53 and 54 of both engines. Valve 54 now vents cylinder 14 to theatmosphere, allowing spring to bring the brake shoes into light contactwith the brake drum. Valve 53 connects line 57 to line 59 so that thebottom end of brake cylinder 13 can now be vented to the atmospherethrough. bleed valve 64. The rate of exhausting air from the brakecylinder is now controlled by the bleed valve through deenergizing itsnormally energized coil 65 by deceleration regulator 10. As the coil isdeenergized, the valve opens, al-

lowing air to escape from line 59 via outlet 66. The regulator includesa rate regulator 73 having a potentiometer 74 for setting a value ofdeceleration for the hoist, and a tachometer 75 driven by the hoist andgenerating an electrical signal representing hoist speed. As the brakesdecelerate the hoist, the voltage from the tachometer generator fallsindirect proportion to the decrease in speed. The rate regulatormonitors these changes in tachometer voltage and when the voltage isequal to or exceeds the set value, the regulator causes valve 64 toclose so as to prevent a further increase in the deceleration rate. Inthe event that the rate of deceleration drops below the set value, theregulator will call for an increase of braking by opening valve 64 for ashort interval. By this means the regulator holds deceleration at theset value. At the instant that the winder comes to rest, the tachometervoltage becomes zero. Sensing this, the regulator causes the brakes tobe fully applied. The regulator is provided witha discriminating circuitby means of which it senses a difference between a decrease'in speed inthe forward direction and an increase in speed in the reverse direction;consequently, even though a few feet of roll back may occur, there is nopossibility of the deceleration regulator interfering with full brakeapplication. During deceleration, the brakes were applied by only one ofthe two cylinders available for braking purposes, as a result, smootherbraking is to be expected than what is possible with an equivalentsingle cylinder engine.

Another advantage inherent in the two cylinder engine over theequivalent single cylinder engine is that emergency stopping will be farless abrupt in the event of regulator failure because one of two smallcylinders is now suddenly applying the brakes rather than one largecylinder. In other words, only one-half of the total braking capacity issuddenly activated for the emergency stop. The regulator is fail safe inthat valve 64 is normally open and must be energized from the regulatorto hold off some of the braking effort that it would otherwise allow.Deenergizing coil 65 allows valve 64 to open fully, and this allows theair to escape freely from the lower end of cylinder ll3 via lines 60 and57, valve 53, line 59, valve 64 and outlet 66. Hence cylinder 13immediately applies the brakes fully without any control of the rate ofapplication. Even though cylinder 13 applies the brakes at anuncontrolled rate, they are applied far less harshly than they would bewith the entire braking capacity active as would be the case with abraking engine having but one cylinder. Hence, with the two cylinderengine,'regulator controlled deceleration as well asuncontrolledemergency' braking are much to be preferred over that of thesingle cylinder engine.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

lclaim:

l. in a system for braking a hoist, a set of brakes for braking thehoist and a pneumatic engine for operating the brakes, said enginecomprising a source of compressed air; at least two brake actuatorsoperated by said compressed air; means for coupling said actuatorstogether and to said brakes for actuation thereof; means for controllingthe air supply to at least one of said actuators for selectivelyapplying or releasing the brakes; means for controlling the air supplyto said other actuators for selectively rendering one or more of theminoperative or operative for assisting said one actuator in applyingbrakes; a relatively heavy weight, another actuator connected directlyto said compressed air source for operation by the compressed air forholding said weight in an elevated position but allowing the weight todescend when the pressure decreases below a predetermined value;mechanicalmeans linking said weight with said brakes for application ofthe brakes by the descending weight; and means for allowing saidactuators fee freedom of braking operation from said weight and thelinkage operatively associated with the weight.

2. in a system for braking a hoist, a set of brakes for braking thehoist and a pneumatic engine for operating the brakes, said enginecomprising a source of compressed air; at least two brake cylinders eachhaving a double acting piston operated by said compressed air; means forcoupling said pistons together and to said brakes such that compressedair in one end of said cylinders urges piston movement for applying thebrakes and compressed air in the other end of said cylinders urgespiston movement for releasing the brakes; air lines connecting said oneend of said cylinders directly to said source of compressed air; atwo-way selector valve for at least one of said cylinders, said valvehaving one way interconnecting the two ends of the cylinder and theother way connecting said other end of the cylinder to an air line meanswhich is also connected to said other ends of the remaining cylinders; atwo-way flow control valve having one way connecting said air line meansto said source of compressed air and the other way connecting said airline means to the atmosphere; a relatively heavy weight; anothercylinder having a single acting piston supporting said weight; anotherair line connecting said source of compressed air directly to one end ofsaid other cylinder so the air therein causes the piston to hold theweight in an elevated position; mechanical means linking said weightwith said brakes for application of the brakes by the descending weightwhen the air pressure decreases below a predetermined value; and meansfor allowing said double acting pistons freedom of braking movement fromthe elevated weight and its linkage with the brakes.

3. In a system for braking a hoist, a set of brakes for braking thehoist and a pneumatic engine for operating the brakes, said enginecomprising a source of compressed air; two brake cylinders each having adouble acting piston operated by said compressed air; means for couplingsaid pistons together and to said brakes such that compressed air in oneend of said cylinders urges piston movement for applying the brakes andcompressed air in the other end of said cylinders urges piston movementfor releasing the brakes; air lines connecting said one end of saidcylinders directly to said source of compressed air; a two-way selectorvalve for one of said cylinders, said valve having one wayinterconnecting the two ends of the cylinder and the other wayconnecting said other end of the cylinder to an air line means which isalso connected to said other end of the other cylinder; a two-way flowcontrol valve having one way connecting said air line means to saidsource of compressed air and the other way connecting said air linemeans to the atmosphere; a relatively heavy weight; another cylinderhaving a single acting piston supporting said weight;

another air line connecting said source of compressed air directly toone end of said other cylinder so the air' therein causes the piston tohold the weight in an elevated position; mechanical means linking saidweight with said brakes for application of the brakes by the descendingweight when the air pressure decreases below a predetermined value; andmeans for allowing said double acting pistons freedom of brakingmovement from the elevated weight and its linkage with the brakes.

4. The braking engine defined in claim 2 wherein said flow control valveis a servovalve operated pneumatically from manual controls.

The braking engine defined in claim 2 wherein said air line meansincorporates a two-way selector valve normally having one way in saidair line means and in its other position disconnecting the air linemeans from the flow control valve and connecting it to a bleed valvevented to the atmosphere, and a hoist deceleration regulator forcontrolling the rate that the bleed valve exhausts air from the linemeans.

6. The braking engine defined in claim 2 wherein a compressed aircylinder is provided for releasing the brakes, said cylinder having asingle acting piston coupled to said double acting pistons and havingone end connected to said air line means so compressed air from the lineurges the piston to release the brakes; and wherein there is alsoprovided a coil spring compressed by the release cylinder whilereleasing the brakes.

7. ln a system for braking a hoist, a set of brakes for braking thehoist and a pneumatic engine for operating the brakes, said enginecomprising a source of compressed air; two brake cylinders each having adouble acting piston operated by said compressed air; means for couplingsaid pistons together and to said brakes such that compressed air in oneend of said cylinders urges piston movement for applying the brakes andcompressed air in the other end of said cylinders urges piston movementfor releasing the brakes; air lines connecting said one end of saidcylinders directly to said source of compressed air; a two-way selectorvalve for one of said cylinders, said valve having one wayinterconnecting the two ends of the cylinder and the other wayconnecting said other end of the cylinder to another air line which isalso connected to said other end of the other cylinder; a bleed valveconnected to said other air line for exhausting air therefrom; and aregulator for controlling said bleed valve whereby the air exhaustedfrom said other line is controlled by said regulator.

8. The braking engine defined in claim 7 wherein said bleed valve isnormally open and its closing is controlled by said regulator.

9. The braking engine defined in claim 7 wherein said bleed valve isnormally open valve electrically operated for closing from saidregulator, and said regulator is an electrical control device forproducing an electrical output proportional to hoist deceleration, theextent of valve closing being proportional to the magnitude of saidelectrical output.

[0. In a system for braking a hoist, a set of brakes for braking thehoist and a pneumatic engine for operating the brakes,

said engine comprising a source of compressed air; two brake cylinderseach having a double acting piston operated by said compressed air;means for coupling said pistons together and to said brakes such thatcompressed air in one end'of said cylinders urges piston movement forapplying the brakes and compressed air in the other end of saidcylinders urges piston movement for releasing the brakes; air linesconnecting said one end of said cylinders directly to said source ofcompressed air; a two-way selector valve for one of said cylinders, saidvalve having one way interconnecting the two ends of the cylinder andthe other way connecting said other end of the cylinder to another airline which is also connected to said other end of the other cylinder; adeceleration regulator for controlling the braking of said hoistaccording to the deceleration thereof; means operated manually forcontrolling the braking of said hoist; and another two-way selectorvalve connected by air lines to said regulator; said manual controlmeans and said other air line for selectively connecting saiddeceleration regulator or said manual control means to said other airline.

11. In a system for braking a hoist, a set of brakes for braking thehoist and a pneumatic engine for operating the brakes, said enginecomprising a source of compressed air; two brake cylinders each having adouble acting piston operated by said compressed air; means for couplingsaid pistons together and to said brakes such that compressed air in oneend of said cylinders urges piston movement for applying the brakes andcompressed air in the other end of said cylinders urges piston movementfor releasing the brakes; air lines connecting said one end of saidcylinders directly to said source of compressed air; a two-way selectorvalve for one of said cylinders, said valve having one wayinterconnecting the two ends of the cylinder and the other wayconnecting said other end of the cylinder to another air line which isalso connected to said other end of the other cylinder; a decelerationregulator for controlling the braking of said hoist according to thedeceleration thereof; a servovalve having first and second main portsand a vent port; another two-way selector valve connected by air linesto said regulator said first port of the servovalve and said other airline for selectively connecting said deceleration regulator or saidservovalve to said other air line; an additional air line connectingsaid second port of the servovalve to said source of compressed air; andmanually operated means for controlling said servovalve for selectivelyallowing compressed air to flow from said second port to said first portor from said first port to said vent port.

12. The braking engine defined in claim 11 wherein said manuallyoperated control valve is supplied with compressed air from said sourceof compressed air and connected to said servovalve for control thereofin response to manual manipulation of the control valve.

13. The braking engine defined in claim 11 wherein said other air lineis connected to one side of a power actuated offon valve which has itsother side vented to the atmosphere, said off-on valve being closed whenenergized and open when deenergized.

1. In a system for braking a hoist, a set of brakes for braking thehoist and a pneumatic engine for operating the brakes, said enginecomprising a source of compressed air; at least two brake actuatorsoperated by said compressed air; means for coupling said actuatorstogether and to said brakes for actuation thereof; means for controllingthe air supply to at least one of said actuators for Selectivelyapplying or releasing the brakes; means for controlling the air supplyto said other actuators for selectively rendering one or more of theminoperative or operative for assisting said one actuator in applyingbrakes; a relatively heavy weight, another actuator connected directlyto said compressed air source for operation by the compressed air forholding said weight in an elevated position but allowing the weight todescend when the pressure decreases below a predetermined value;mechanical means linking said weight with said brakes for application ofthe brakes by the descending weight; and means for allowing saidactuators fee freedom of braking operation from said weight and thelinkage operatively associated with the weight.
 2. In a system forbraking a hoist, a set of brakes for braking the hoist and a pneumaticengine for operating the brakes, said engine comprising a source ofcompressed air; at least two brake cylinders each having a double actingpiston operated by said compressed air; means for coupling said pistonstogether and to said brakes such that compressed air in one end of saidcylinders urges piston movement for applying the brakes and compressedair in the other end of said cylinders urges piston movement forreleasing the brakes; air lines connecting said one end of saidcylinders directly to said source of compressed air; a two-way selectorvalve for at least one of said cylinders, said valve having one wayinterconnecting the two ends of the cylinder and the other wayconnecting said other end of the cylinder to an air line means which isalso connected to said other ends of the remaining cylinders; a two-wayflow control valve having one way connecting said air line means to saidsource of compressed air and the other way connecting said air linemeans to the atmosphere; a relatively heavy weight; another cylinderhaving a single acting piston supporting said weight; another air lineconnecting said source of compressed air directly to one end of saidother cylinder so the air therein causes the piston to hold the weightin an elevated position; mechanical means linking said weight with saidbrakes for application of the brakes by the descending weight when theair pressure decreases below a predetermined value; and means forallowing said double acting pistons freedom of braking movement from theelevated weight and its linkage with the brakes.
 3. In a system forbraking a hoist, a set of brakes for braking the hoist and a pneumaticengine for operating the brakes, said engine comprising a source ofcompressed air; two brake cylinders each having a double acting pistonoperated by said compressed air; means for coupling said pistonstogether and to said brakes such that compressed air in one end of saidcylinders urges piston movement for applying the brakes and compressedair in the other end of said cylinders urges piston movement forreleasing the brakes; air lines connecting said one end of saidcylinders directly to said source of compressed air; a two-way selectorvalve for one of said cylinders, said valve having one wayinterconnecting the two ends of the cylinder and the other wayconnecting said other end of the cylinder to an air line means which isalso connected to said other end of the other cylinder; a two-way flowcontrol valve having one way connecting said air line means to saidsource of compressed air and the other way connecting said air linemeans to the atmosphere; a relatively heavy weight; another cylinderhaving a single acting piston supporting said weight; another air lineconnecting said source of compressed air directly to one end of saidother cylinder so the air therein causes the piston to hold the weightin an elevated position; mechanical means linking said weight with saidbrakes for application of the brakes by the descending weight when theair pressure decreases below a predetermined value; and means forallowing said double acting pistons freedom of braking movement from theelevated weight and iTs linkage with the brakes.
 4. The braking enginedefined in claim 2 wherein said flow control valve is a servovalveoperated pneumatically from manual controls. ,5 The braking enginedefined in claim 2 wherein said air line means incorporates a two-wayselector valve normally having one way in said air line means and in itsother position disconnecting the air line means from the flow controlvalve and connecting it to a bleed valve vented to the atmosphere, and ahoist deceleration regulator for controlling the rate that the bleedvalve exhausts air from the line means.
 6. The braking engine defined inclaim 2 wherein a compressed air cylinder is provided for releasing thebrakes, said cylinder having a single acting piston coupled to saiddouble acting pistons and having one end connected to said air linemeans so compressed air from the line urges the piston to release thebrakes; and wherein there is also provided a coil spring compressed bythe release cylinder while releasing the brakes.
 7. In a system forbraking a hoist, a set of brakes for braking the hoist and a pneumaticengine for operating the brakes, said engine comprising a source ofcompressed air; two brake cylinders each having a double acting pistonoperated by said compressed air; means for coupling said pistonstogether and to said brakes such that compressed air in one end of saidcylinders urges piston movement for applying the brakes and compressedair in the other end of said cylinders urges piston movement forreleasing the brakes; air lines connecting said one end of saidcylinders directly to said source of compressed air; a two-way selectorvalve for one of said cylinders, said valve having one wayinterconnecting the two ends of the cylinder and the other wayconnecting said other end of the cylinder to another air line which isalso connected to said other end of the other cylinder; a bleed valveconnected to said other air line for exhausting air therefrom; and aregulator for controlling said bleed valve whereby the air exhaustedfrom said other line is controlled by said regulator.
 8. The brakingengine defined in claim 7 wherein said bleed valve is normally open andits closing is controlled by said regulator.
 9. The braking enginedefined in claim 7 wherein said bleed valve is normally open valveelectrically operated for closing from said regulator, and saidregulator is an electrical control device for producing an electricaloutput proportional to hoist deceleration, the extent of valve closingbeing proportional to the magnitude of said electrical output.
 10. In asystem for braking a hoist, a set of brakes for braking the hoist and apneumatic engine for operating the brakes, said engine comprising asource of compressed air; two brake cylinders each having a doubleacting piston operated by said compressed air; means for coupling saidpistons together and to said brakes such that compressed air in one endof said cylinders urges piston movement for applying the brakes andcompressed air in the other end of said cylinders urges piston movementfor releasing the brakes; air lines connecting said one end of saidcylinders directly to said source of compressed air; a two-way selectorvalve for one of said cylinders, said valve having one wayinterconnecting the two ends of the cylinder and the other wayconnecting said other end of the cylinder to another air line which isalso connected to said other end of the other cylinder; a decelerationregulator for controlling the braking of said hoist according to thedeceleration thereof; means operated manually for controlling thebraking of said hoist; and another two-way selector valve connected byair lines to said regulator; said manual control means and said otherair line for selectively connecting said deceleration regulator or saidmanual control means to said other air line.
 11. In a system for brakinga hoist, a set of brakes for braking the hoist and a pneumatic enginefor operating the brakes, said engine cOmprising a source of compressedair; two brake cylinders each having a double acting piston operated bysaid compressed air; means for coupling said pistons together and tosaid brakes such that compressed air in one end of said cylinders urgespiston movement for applying the brakes and compressed air in the otherend of said cylinders urges piston movement for releasing the brakes;air lines connecting said one end of said cylinders directly to saidsource of compressed air; a two-way selector valve for one of saidcylinders, said valve having one way interconnecting the two ends of thecylinder and the other way connecting said other end of the cylinder toanother air line which is also connected to said other end of the othercylinder; a deceleration regulator for controlling the braking of saidhoist according to the deceleration thereof; a servovalve having firstand second main ports and a vent port; another two-way selector valveconnected by air lines to said regulator said first port of theservovalve and said other air line for selectively connecting saiddeceleration regulator or said servovalve to said other air line; anadditional air line connecting said second port of the servovalve tosaid source of compressed air; and manually operated means forcontrolling said servovalve for selectively allowing compressed air toflow from said second port to said first port or from said first port tosaid vent port.
 12. The braking engine defined in claim 11 wherein saidmanually operated control valve is supplied with compressed air fromsaid source of compressed air and connected to said servovalve forcontrol thereof in response to manual manipulation of the control valve.13. The braking engine defined in claim 11 wherein said other air lineis connected to one side of a power actuated off-on valve which has itsother side vented to the atmosphere, said off-on valve being closed whenenergized and open when deenergized.